Physical Geology Introduction


PHYSICAL GEOLOGY
Fall Semester, 1997
John C. Butler
Room 304 SR I
743-3411
jbutler@uh.edu


The Scientific Method


	Observation


	Attempt To Explain - Hypothesis


	Testing The Hypothesis


	More Observations - Predictions


	Modification of the Hypothesis


	Theory



Physical Geology

"Geology is the science that studies Earth -- how it 
was born, how it evolved, how it works, and how
we can help preserve it."

	Present


	Past


	Evolution


	Future

What is the extent of the relationship between 
internaland external processes and Earth materials?



Observations play a major role in the geosciences.  



Experimental approach, while sometimes desirable is
difficult - TIME




Uniformitarianism


	The present is the key to  the past:

		Process

		Rates

		Actualism

Earth's History is recorded in the materials it is made
 up of:


	Composition - chemistry


	Texture - size, shape, 	arrangement of constituents


	Structures - features - such as layers


	Geologic Setting




 Origin of Planets



	Universe began ~10 to 15 billion years ago - 
	Big Bang Hypothesis


	Since then the universe has expanded to form the 
	galaxies, stars and planets


	Nebular Hypothesis - dust clouds - consist 
	primarily of hydrogen and helium and "dust"


 particles attract each other under the influence of gravity


Stars


 as the dust clouds contract the pressure acting on the 
 hydrogen and helium increases


 at sufficiently high pressures some of the hydrogen
 reactsto form helium - light is emitted


 the chemical elements are formed within the interiors
 of stars


 Minerals


Naturally occurring solids


Inorganic in origin 
	(not part of a life process)


Crystalline arrangement
	(an orderly internal structure)


Fixed composition
	(or variable within fixed limits)




Rocks: Records of Geologic Processes


Rocks are made up of one or more minerals


Three major rock types:



	Igneous



	Sedimentary



	Metamorphic





Igneous - Fire Formed	


	Depending upon the composition of the starting material,
	some liquid may be produced.



	In general, a mixture does not have a unique 
	melting point.



	Mixtures exhibit a melting range



	The magma (liquid) migrates upwards (most liquids 
	are less dense than the solids that produce them)
	and cools.




	Crystals grow from the liquid and compete for space - 
	An Interlocking Texture.




	If cooling takes place at depth an Intrusive Igneous
	Rockis formed



­ Plutonic .... relatively coarse grains





	If cooling takes place at the surface an Extrusive 
	Igneous Rock forms



­ Volcanic ... relatively fine grained




Sedimentary Rocks



	Form at or near the Earthıs surface



	Layered



	The Earth has a reactive atmosphere




		­ Water
	­ Carbon Dioxide
	­ Oxygen 


 Genesis of Sedimentary Rocks


	Physical Weathering- reduction in size





	Chemical Weathering- change in composition




	Transportation


			Solid Particles ... clastics by water, wind, ice


			Ions in Solution ... chemical




	Clastics - particles do not form interlocking texture


	Chemical - grow from solution



	Sedimentary rocks tend to be layered



	The loose grains (sediment) must be converted to 
	sedimentary rock by cementation or compaction




Metamorphic Rocks


	Changed rocks - in response to changes in Temperature
	and Pressure.


	New Minerals may grow



	All rocks can be metamorphosed


The Earth - Compositional Variations ... Heterogeneous	



	0-  40 (miles)  Crust - relatively young
	­ continental crust and oceanic crust



	MOHO separates crust from mantle



	10- 400  Upper mantle



	400-2890 Mantle



	2890-5150  Outer core - Liquid


	5150-6378  Inner core - Solid



The Earth is a Dynamic Planet



	Distribution of Earthquake Epicenters



	Distribution of Volcanoes



	Distribution of Rock Types




Distribution of Rock Types




	Carbonates 



		­ shallow water marine
	­ near the equator
	­ organic



	Coals
	­ plant material ... reducing environment ... 
	metamorphic






The Earth  Post 1960ıs


	Lithosphere - the crust and the upper mantle
  ­ behaves as a RIGID solid





	Asthenosphere - from the lithosphere down to some 
	400 miles ­ behaves as a PLASTIC substance




Excess Heat	



	Temperature - function of motion of molecules/ions


	Heat - ³that which flows when two bodies at 
	differenttemperatures are brought in contact.


	Heat - Conduction ... heat flows by the 
	increased vibration
	 of ions/molecules

	Convection ... physical movement of a fluid 
	(including air) driven by a temperature gradient


	Radiation ... from hot object ... part of 
	the electromagnetic spectrum


Behavior At Boundaries	



	Extensional - Tension - pull apart





	Compressional - push together




	Transform - slide past one another